As can be seen from U.S. Pat. Nos. 2,486,282, 3,082,132, 3,846,189, 3,401,035, 2,395,608 and 3,598,660, heat treating processes for various steels to alter their physical properties such as hardness, machinability and brittleness, are generally known in the art. However, there is still a need for a process to alter the hardness of very hard, as cast, high chromium, high carbon stainless steels to make them more readily machinable. Heretofore, the difficulty of machining steels such as those containing from 1 to 2% carbon, 12 to 18% chromium, 1 to 2% molybdenum and normal amounts of other elements such as silicon, boron and the like, the balance being substantially iron, has restricted their use to the as cast form. An example of such a steel which typically has a Rockwell hardness of C60-C62 is Zevescal W, manufactured by Columet Steel Casting Corporation. This steel has the following composition: C--2.0%, Cr--16.0%, Mo--1.75%, Si--1.0%, B--trace, the balance being iron.
By treating such steel in accordance with this invention, I have surprisingly discovered that the hardness can be reduced to as low as C20-C30 making it possible to readily machine any cast parts, thereby expanding the potential uses of the steel. By further thermal treatment, as disclosed herein, the steel can be rehardened after machining to a hardness of about C60 where it exhibits excellent wear characteristics.